This application is a division of application Ser. No. 246,715, filed Apr. 24, 1972 now U.S. Pat. No. 3,894,294.
The present invention relates generally to self-processing photographic cameras of the reflex type and, more particularly, to a reflex camera in which a specular surface is moved into the optical path of a taking lens when the camera is caused to assume an exposure mode configuration.
Certain photographic film materials are structured to directly record a positive image of any subject properly imaged and exposed thereon. Exemplary of such materials are the film units described in U.S. Pat. No. 3,415,644, entitled "Novel Photographic Products and Processes" and issued to E. H. Land on Dec. 10, 1968. Film units of this type are intended for use within the above-noted selfprocessing photographic cameras and incorporate all of the materials necessary to produce a positive photographic print immediately following their exposure. While being of a somewhat complex chemical makeup, the film units are physically structured to include a planar photosensitive element in laminar combination with a transparent image-receiving element. Specially packaged processing units are additionally included within the units.
To image properly through a lens system upon the above-described film units, it is necessary that one or an odd number of specular surfaces be incorporated within the optical path extending from the camera lens to the exposure plane of the film unit. Although the film units are configured to provide a desirably large film format, certain improved photographic camera designs have taken advantage of the requisite specular surface to achieve somewhat compact overall camera structures.
Improved photographic cameras as above described are intended to perform in fully automated fashion while being structured so thinly and compactly as to be carried conveniently in the pocket of a garment. Typically, these improved cameras incorporate an optimum viewing and focusing system together with fully automatic exposure control and motorized automatic film processing. In effect, the fully automatic camera represents an instrumentality incorporating a complex, multi-step process control system.
For purposes providing optimum viewing performance as well as structural compactness, the automated camera preferably utilizes a form of single lens reflex viewing. As described and claimed in a copending application for Letters Patent by E. H. Land, entitled "Reflex Camera", filed Apr. 14, 1970, Ser. No. 28,567, and commonly assigned herewith now U.S. Pat. No. 3,672,281, such reflex cameras normally assume a viewing-focusing mode configuration in which their exposure plane is isolated from scene illumination by a flat, movable operator or mirror and viewing surface assembly. In a viewing configuration, the operator assembly serves a function of providing a surface upon which a scene, in reflex fashion, may be framed and focused in preparation for the photographic exposure. In accordance with a modified single lens optical operation, depression of a start button on the camera commences a multi-step control causing its components to assume an orientation securing an exposure chamber by closing its shutter through an electromagnetic drive system. When this chamber is secured, the camera is caused to commence an exposure mode operation in which the earlier-described operator assembly is released for movement via a spring drive to uncover the exposure plane and provide a revised reflex optical path for subsequent exposure of the previously imaged scene.
As an exposure mode configuration is achieved, the automatic exposure control sub-system of the camera cycles through a regulated exposure interval following which the shutter again closes to secure the exposure chamber. The control system of the camera is then called upon to block the operator assembly by driving it via an electrical motor into its viewing mode configuration. Prior to termination of the photographic cycle, an exposed photosensitive film unit is automatically removed from its position at the exposure plane and drawn through a motor-driven processing station. When the operator assembly has been cocked and returned to its orientation covering the exposure plane, the shutter is again opened to its maximum extent and the camera is ready for its next succeeding photographic cycle.
As mentioned previously, the operator assembly is cocked by driving it via an electrical motor into its viewing mode configuration. As a consequence, the operator assembly drive system will usually require an override form of drive linkage to assure proper seating at its cocked position. Such override feature is extremely difficult to incorporate into the confined housings of compact cameras without resorting to the use of relatively high-torque rate drive springs with their attendant undesirably high loads on the relatively small drive motor.
If the operator assembly encounters any interference during its movement toward its cocked or viewingfocusing mode position, the motor may be over-loaded and damaged. Certainly, if the motor is over-loaded enough, the power drain upon a power supply such as a battery may render it incapable of carrying out other functions during a given photographic cycle.
In dealing with some of the foregoing problems, certain prior art photographic cameras such as described in copending application Ser. No. 103,219, filed Dec. 31, 1970, and commonly assigned herewith (now U.S. Pat. No. 3,685,416), incorporate a lost-motion connection within the drive system for moving the operator assembly between the exposure mode position and the viewing mode position. Movement of the operator assembly between these positions is accomplished through a system incorporating a four-bar linkage and a drive spring. The system is configured to minimize the time required for moving the operator assembly to its exposure mode position whilst also minimizing the elastic rebound of the operator assembly when it reaches its exposure mode position.
Typically, a torsion spring is employed for moving the operator assembly to its exposure mode position. The torsion spring is prewound to minimize the operator assembly movement time and also reduce its elastic rebound upon reaching the exposure mode position. This is achieved by maximizing the residual torque of the drive spring at the exposure mode position of the operator assembly.
A prewound override torsion spring is provided within the drive system and is configured to serve a dual purpose. The override spring functions to insure that the operator assembly is fully seated in its viewing position by allowing the motor to remain energized for a select interval following the seating of the assembly. The override spring absorbs the resultant over-travel motion and biases the assembly into its viewing mode position. This permits more easily achieved manufacturing tolerances in the assembly return mechanism since the components thereof do not have to cooperate to move the operator assembly the precise distance between the exposure mode position and the viewing mode position.
Additionally, the override spring serves to provide an override or lost-motion connection between the motor and the operator assembly. If the operator assembly encounters any interference during its motor-driven movement between the exposure and viewing mode positions, the override spring will allow the motor to finish its normal return cycle. The energy from the motor will be transferred to and stored in the override spring until such time as the interference is removed. When the interference is removed, the override spring returns the operator assembly to its viewing position and attendant damage to the motor will be alleviated.
The override torsion spring described hereinabove which is used in the device of U.S. Pat. No. 3,685,416, aforesaid, is disposed concentrically within the low-rate torsional drive spring employed for moving the operator assembly to its erected position. Obviously, the entire mechanism is somewhat complicated and difficult of assembly.
Inasmuch as the operator assembly is spring driven from its viewing-focusing mode position to its exposure mode position in a relatively brief period of time, the operator assembly is subject to undersired oscillation or "bounce" upon reaching its exposure mode position. Obviously, rapid movement of the operator assembly from its viewing-focusing mode position to its exposure mode position is necessary to assure that an acceptably small time interval takes place between the activation of the start button by the operator until the commencement of the exposure of the film unit. Further, unless the bounce of the operator assembly upon reaching the exposure mode position can be ameliorated, it is necessary to provide an undesired delay interval between the reaching of the exposure mode position by the operator assembly and the commencement of a photographic exposure in order to provide sufficient time for the operator assembly to cease its undesired oscillation. Undesired oscillation of the operator assembly such as described hereinabove will result in altering the optical path from the taking lens to the film plane so as to cause the image to be out of focus resulting in an unacceptable photographic exposure.
It will be recalled that a prewound torsion spring is utilized to erect the operator assembly in the prior art photographic cameras such as described in U.S. Pat. No. 3,685,416, supra. It is characteristic of a torsion spring that the torque delivered thereby decreases from its initial value to a lesser magnitude as the torsion spring delivers its energy to the driven member. If the torsion spring is designed to provide a sufficiently large torque when the driven member reaches its desired position, it may function to secure the driven member (in this case the operator assembly) in such desired position in a manner preventing any undesired elastic rebound or bounce thereof. Naturally, the higher the initial torque delivered by the torsion spring, the higher will be the remaining torque supplied by such spring when the driven member reaches its desired position. However, if the initial torque of the torsion spring is made too great (as by highly preloading the torsion spring) then the other components of the system for erecting the driven member may be unduly stressed and an attendant loss of efficiency may be engendered, also. One technique for assuring that the torque delivered by the torsion spring does not drop off too quickly when the driven member is moved from its initial position to its desired position is to utilize what is known as a low-rate torsion spring. Such a spring contains many coils and the torque delivered thereby changes relatively slowly as the torsion spring unwinds. Nevertheless, in order to provide an acceptably high torque from the torsion spring to the operator assembly when the operator assembly has reached the exposure mode position, it is necessary to provide a relatively high preload to the torsion spring which, as indicated supra, may have a deleterious effect on the other components of the operator assembly drive system.